4.2.2 Forecasting Bandwidth consumption – residential access
The bandwidth requirement for a TDM-PON is a function of the aggregated bandwidth demand
of all the subscribers on that PON. A statistical model, described in [eh1] and [eh3], forecasts
aggregate residential downstream bandwidth demands. Since it is not possible to predict the
future with certainty, the model attempts to bound the forecast with a “moderate” set of inputs
and a “heavy” set of inputs. The heavy inputs, in relation to the moderate inputs, assume more
concurrent video streams per home, relatively higher penetration of HD and UHD displays and
higher availability of HD and UHD content, lighter video compression for improved video
quality, and larger and faster growing burst traffic. In both scenarios, it is most appropriate for
NG-EPON to be able to support the “worst case” where all video traffic, including all linear TV
(i.e., traditional scheduled non-time-shifted television service), is unicasted in band. Peak-hour
forecasts for both the moderate and heavy demand scenarios are presented in Figure 1. By far,
most of the demand results from managed plus OTT video traffic.
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Aggregated demand (Mb/s)
1000
128 subscribers
64 subscribers
32 subscribers
16 subscribers
100
2014
2016
2018
2020
2022
2024
Aggregated demand (Mb/s)
(a) Moderate demand scenario
128 subscribers
1000
64 subscribers
32 subscribers
16 subscribers
100
2014
2016
2018
2020
2022
2024
(b) Heavy demand scenario
Figure 1: Forecasted DS demand vs. the number of aggregated subscribers, peak hour
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The aggregated downstream demands in Figure 1 include peak-hour sustained bandwidth
demand and peak-hour average burst bandwidth demand. To complete the demand picture, it is
necessary to add the maximum individual peak burst demand, which requires additional
bandwidth for headroom. The magnitude of this headroom must at least accommodate a
successful speed test run by a subscriber receiving the maximum service level offered. This is
required because subscribers will expect to pass a speed test even during peak hour traffic (the
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case where multiple subscribers run a speed test simultaneously is neglected). For example, in
the heavy demand scenario, for 32 subscribers on a TDM-PON, there will be approximately
1 Gb/s of downstream peak hour traffic in the year 2024. If 1 Gb/s service is to be offered over
this PON, then 1 Gb/s of bandwidth headroom is required to support peak bursts of 1 Gb/s, for a
total aggregate downstream bandwidth demand of 2 Gb/s during peak hour.
The above forecast indicates that 10G-EPON can support downstream residential bandwidth
demands plus a 1 Gb/s service offer up to the year 20241. WDM-PON FTTH systems, with at
least 1 Gb/s dedicated bandwidth per wavelength, could also support 1 Gb/s service. There is no
differentiation on this point among these FTTH technologies.
Therefore, perhaps the most important bandwidth differentiation that can be offered by NGEPON for residential services is the peak hour downstream bandwidth headroom, which
determines the maximum burst demand that can be supported and therefore the maximum
downstream service level that an operator can offer. For TDM-PON MAC domains, this can be
determined by simply subtracting the forecasted aggregate downstream demand in Figure 1 from
the TDM-PON MAC downstream bandwidth capacity (less overheads). For existing and NGEPON candidate FTTH technologies, the maximum downstream service levels that can be
offered in the year 2024 are indicated in Figure 2.
1
If, instead of a statistical view a “worst-case” view is preferred, a 10G-EPON could support 32 subscribers, each
streaming four simultaneous streams of UHD-2 “8k” video at 50 Mb/s each, and still have enough headroom to
support bursts, and therefore a service offer, of more than 2 Gb/s.
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Peak-hour bandwidth headroom (Gb/s)
40
35
30
25
20
15
10
5
0
WDM-PON
1 Gb/s/λ
GPON
32 subs
10G EPON
32 subs
MSD-WDM-PON MSD-WDM-PON
10 Gb/s/λ
10 Gb/s/λ
32 subs
8 subs
WDM-PON
10 Gb/s/λ
TDM-PON
25 Gb/s
32 subs
TDM-PON
40 Gb/s
32 subs
Figure 2: Peak-hour bandwidth headroom = maximum service level that can be offered for existing
and NG-EPON candidate access technologies in year 2024 (*32 subscribers per PON).
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Figure 2 indicates, from a downstream residential bandwidth point of view, that to significantly
differentiate itself from existing 10G EPON, an NG-EPON system will need to support more
than 10 Gb/s service. In other words, a TDM-PON MAC must support an aggregate bit rate or a
WDM-PON must support a per-wavelength bit rate of more than 10 Gb/s.
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